1. Field of the Invention
The invention relates to the field of waveguides in photonic crystals and in particular to different methods for controlling the positions of the guided modes of the photonic crystal waveguides.
2. Description of the Prior Art
The tasks of generation, guiding and detection of the lightwave signals are fundamental tasks in any optical system. Ideally, in order to make small scale, all optical signal processing devices, it is necessary to have the components that are doing each of these tasks integrated on one chip. Photonic crystals introduced in the recent years, are thought to be promising candidates for achieving this high level of integration. Due to the difficulties associated with the fabrication of three dimensional photonic crystals, planar photonic crystals have attracted significant research attention.
The basis of the planar photonic crystal is a dielectric slab, perforated with a two dimensional periodic lattice of holes. The symmetry of the lattice (triangular, square, etc.) plays a crucial role and determines the properties of the planar photonic crystal. Due to the periodicity of the lattice, frequency bandgaps for guided modes of the slab are opened, and light of certain frequencies can not propagate in the slab. The light is localized to the slab in the vertical direction by means of total internal reflection (TIR) and is controlled in the lateral direction by the two dimensional photonic crystal. The combination of these two mechanisms makes localization of light in all three dimensions possible.
Photonic crystal waveguides have attracted attention since they were first proposed. The most interesting property of the photonic crystal waveguide is the possibility of making sharp bends, with acceptable transmission efficiency around the bend. So far, many groups have investigated different properties of the photonic crystal waveguides. In most of these studies, waveguides were defined as single-or multi-line defects in the photonic crystal lattice formed by removing one or more rows of holes. Modal analysis of this type of waveguide show that they are multimode. Recently, a novel way of reducing the number of modes in the waveguide has been proposed and analyzed in two dimension. Experimental characterization of guiding in photonic crystal waveguides was also reported by several groups.
What is needed is the ability to control the position of the guided modes within a frequency bandgap of surrounding planar photonic crystal in order to achieve three important goals: efficient guiding of light, efficient coupling of the light from an external light source into the waveguide and efficient coupling of different photonic crystal devices.